Tuberculosis remains a major infectious disease killer globally, with 9 million new cases and 2 million deaths annually according to the World Health Organization. Resistance to tuberculosis drugs has increased in the last 15 years, and mortality rates from multidrug resistant tuberculosis (MDR IB-defined as resistance to both first line drugs Isoniazid (INH) and rifampin (RIF)) are high in both HIV infected and uninfected persons. Preventing the development of disease in people who have been exposed to MDR TB is the most efficient way to halt transmission to uninfected persons, however traditional treatment for latent TB infection is with INH, and current recommended treatment for MDR TB LTBI is with oflaxacin, a quinalone with relatively weak activity against Mycobacterium tuberculosis. New methods of preventing development of disease in people exposed to MDR TB are vital. This project is a randomized trial of two treatment regimens for latent TB infection of contacts of patients with MDR TB. We will randomize 220 patients to receive moxifloxacin (moxi) alone for 6 months vs. ofloxacin/EMB for 6 months, with outcomes of safety, tolerablility and effectiveness. We hypothesize that moxi alone will have few adverse events, higher completions rates, and similar efficacy vs. ofloxacin/EMB. Administrative and biostats/data management cores will support this study. These trials will contribute to improving our understanding of the control of TB worldwide.